No, the lens itself is glass, but the rest of the housing looks plastic to me – look at the crack/scratch at the last picture. The ring on the 3rd picture appears to be metal.
I don’t know – that’s why I posted those pics to get more opinions.

NikoDoby

Whatever it’s made of, image quality looks good from this lens so far.
Gotta keep cost down somehow, but it is kinda disappointing to see nothing but plastic parts.

Of course it is plastic. Manufacturing the tube and all the gear inside from stainless steel or brass would be awfully expensive — not because steel is expensive, but it costs much more to make CNC tools for “carving” every part instead of pressing them out of plastic material.
Though it’s sad to see that the gearing looks like plastic as well (used for focusing) – 4th picture, on the left. They’ll easily wear out like the cheap Sigma lenses.
By the way, e.g. Nikon also makes plastic zoom lenses, and they work, so maybe it’s not so much a problem — if the lens is cheap. 🙂

Cheap Sigma lenses? I can’t tell if you actually mean the cheaper Sigma lenses or if you’re calling Sigma lenses cheap. In any case, do you mean their EX line as well?

Marvin8

Looks like it’s made to withstand high impact strikes from cottonballs.

m4/3

It is a bit unfair to criticise it for being made from plastic. Nearly all lenses in it’s price range are made from plastic, just look at any canon or nikon lens for that price… some of these lenses last for years under normal use, why would you really need an all metal construction?

Rob-L

I agree m4/3 – My Nikon kit lens was all plastic. I don’t know what everyone is going on about. It shouldn’t a shock to anyone.

Dan

Plastic is good! It just doesn’t sound very good (try ‘engineering plastic’, ‘synthetic’ or ‘polycarbonate’ if that is a concern). But it is strong and durable, light-weight (to its user as well as to the lens mount and focus motor), it doesn’t dent, bend or scratch easily, doesn’t change volume or shape when the temperature changes, isn’t cold to the touch, doesn’t permanently attach itself to your filters, and it is affordable. What’s not to like?

Stephen

I’m all for plastic. Besides all the reasons Dan mentions, it can actually be more impact resistant than metal. To get metal as lite as plastic you have to use metals like titanium and the like. Most of these metals, while hard and durable, are extremely expensive. Also, many of the new “plastic” materials out there are super impact resistant. They also give some, thus reducing the impact that is transferred to the components that mater. It kind of the same principle as why the F1 race cars shatter upon impact. I would rather have some bending and flexing and even a little cracking if it mean the lens is still going to work after a bad fall. As much as we don’t want to admit it, everyone of has dropped a lens. You put it on just hoping that it will still work. Sure, the zoom may not be smooth, but hey it works. Good plastics will solve a lot of dropping issues.